Tunable laser resonance Ram spectroscopy will be used as a selective probe of the structure and the interactions prevalent within the chromophore of rhodopsin during the visual process. We will extend our preliminary studies on dark-adapted bovine rhodopsin to verify our model of rhodopsin based on the resonance Raman data. The approach which this proposal suggests is to study the thermal intermediates of rhodopsin using the resonance Raman technique. Such an investigation will not only test our model of rhodopsin but it will also lay the foundation for a detailed understanding of the structural and electronic nature of the cis-trans isomerization of the retinylidene chromophore - the primary photochemical act in vision. Finally the experiments outlined will contribute a major step to our overall objective which is to study the Raman spectrum of rhodopsin in a living eye during the visual process and to couple, through Raman spectroscopy, discrete molecular changes in the retina with electrophysiological responses.